Disk drive device and clearance control method thereof

The instant nonprovisional patent application claims priority to Japanese Patent Application No. 2007-311773 filed Nov. 30, 2007 and which is incorporated by reference in its entirety herein for all purposes.

Disk drive devices using various kinds of disks, such as optical disks, magneto-optical disks, flexible magnetic disks, and the like have been known in the art. In particular, hard disk drives (HDDs) have been widely used as storage devices of computers and have been one of indispensable storage devices for current computer systems. Moreover, the HDDs have found widespread application to moving image recording/reproducing apparatuses, car navigation systems, cellular phones, and the like, in addition to the computers, due to their outstanding characteristics.

A magnetic disk used in an HDD has multiple concentric data tracks and servo tracks. Each servo track is constituted by a plurality of servo data containing address information. Each data track includes multiple data sectors containing user data. Data sectors are recorded between servo data located discretely in the circumferential direction. A head element portion of a head slider supported by a swing actuator accesses a desired data sector in accordance with address information in the servo data to write data to and retrieve data from the data sector.

In order to increase recording density of a magnetic disk, it is important to decrease the clearance (fly-height) between the head element portion flying over the magnetic disk and the magnetic disk, and to decrease the variation of the clearance; some mechanisms have been proposed to control the clearance. One of such mechanisms has a heater in a head slider; the heater heats the head element portion to adjust the clearance (for example, refer to Japanese Patent Publication No. 2006-190454 “Patent Document 1”). In the present specification, it is called thermal fly-height control (TFC). The TFC generates heat by applying electric current to the heater to make the head element portion protrude by thermal expansion. This reduces the clearance between the magnetic disk and the head element portion. Another mechanism has been known that uses a piezo element to adjust the clearance between the magnetic disk and the head element portion.

The clearance varies with change in barometric pressure (altitude) as well as change in temperature (for example, refer to Japanese Patent Publication No. 2006-92709 “Patent Document 2”). If the clearance preset value in a read/write operation is 5 nm or more, the clearance variation caused by altitude change can be absorbed by a clearance margin. However, if the clearance is not more than 2 or 3 mm in a read/write operation, clearance control for pressure change in addition to temperature change is demanded.

Typical TFC makes a head element portion protrude due to thermal expansion by increasing heater power in response to a decrease in temperature to compensate for the increase in clearance caused by the decrease in temperature. In contrast, as the altitude gets higher and the barometric pressure (hereinafter, referred to as pressure) becomes lower, the fly-height of a slider lowers. The lowered pressure reduces the clearance between the head element portion and the magnetic disk. Therefore, if the temperature is constant, the TFC decreases the protruding amount with decrease in pressure.

An HDD has a number of preset parameters for temperature; accurate temperature sensing is indispensable for normal operation of the HDD. Therefore, a common HDD comprises a temperature sensor as a means to sense the temperature. Similarly, a barometric sensor (altitude sensor) has been known as a means for sensing the pressure. However, use of a barometric sensor increases the number of components in the HDD and the cost of the HDD significantly as well. Since there are few parameters for the pressure to be set except for the parameters for clearance control, it is preferable to determine the pressure without using a barometric sensor.

As described above, the clearance varies with pressure. Accordingly, referring to the clearance allows measurement of a variation in pressure. Some techniques to determine the clearance have been known. A typical technique determines a clearance (a variation in clearance) from the amplitudes of read signals of a head element portion. As the clearance decreases, signal strength increases and the gain of a variable gain amplifier decreases.

Accordingly, referring to a gain of the variable gain amplifier allows determination of the signal strength and the clearance. A technique for determining a more precise clearance determines the clearance from resolving power (resolution) in frequency components of read signals. In another way, the pressure can be estimated from the current value in a spindle motor (SPM) although the result is inferior in accuracy.

For clearance control depending on the pressure without using a barometric sensor, it is necessary to determine a clearance variation by referring to operational parameters in an HDD (the gain in a variable gain amplifier, SPM current values, and the like) like the above-described method. However, the accuracy and reliability in pressure measurement using operational parameters in an HDD are not as high as the ones using a barometric sensor. Inaccurate pressure measurement leads to incorrect clearance control which may cause head-disk contact to damage a head slider or a magnetic disk, or leads to a read/write operation without a requisite clearance margin to cause a hard error (unrecoverable error) due to head-disk contact.

Embodiments of the present invention help to precisely control the clearance between a head and disk for the pressure without using a barometric sensor. In an embodiment of the present invention, an HDD determines a clearance from variations in operational parameters, and further determines a variation in pressure by deducting the clearance variation caused by a variation in temperature from the clearance. When the HDD controls the clearance in accordance with the pressure change, the HDD checks for head-disk contact. The accuracy and reliability in pressure measurement (clearance measurement) using operational parameters are not high. Therefore, confirming the pressure measurement by the presence or absence of head-disk contact eliminates head-disk contact in the following read/write operation to attain a securer margin for the clearance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically depicting an entire configuration of an HDD in one embodiment.

FIG. 2 is a cross-sectional view schematically illustrating a configuration of a head slider having a heater for TFC in one embodiment.

FIGS. 3(a) and 3(b) are drawings schematically illustrating the relationship between the measured results of the altitude change (variation in pressure), the check for head-disk contact, the reference range for determining the necessity of the check.

FIG. 4 is a flowchart illustrating processes of pressure measurement and check for head-disk contact in one embodiment.

FIG. 5 is a block diagram showing logic components for measuring the pressure and checking for head-disk contact in one embodiment.

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